This invention relates generally to a lubrication system enabling ceramic bearing means to resist mechanical wear at elevated temperatures up to 600.degree. C. and higher, and more particularly to continuously supplying metal oxide lubricants during bearing operation as the means for doing so.
Lubrication is a well recognized means to reduce friction and wear between bearing surfaces in dynamic physical contact. Two major areas for which improved lubricants are needed for continued progress are metal forming and transportation. Better metal forming capabilities to minimize machining and grinding require lubrication techniques and lubricants that can be used effectively at temperatures approaching the melting points of the metals now employed. In transportation, one of the most productive areas for increasing energy efficiencies is often referred to as high temperature engines wherein temperatures range from 600.degree. C. and above making the selection of lubricants and means of lubrication still difficult. A known technique for lubricating at such high temperatures is the use of solid lubricants in the form of plasma sprayed coatings of the metals and ceramics being employed. More recent developments whereby an adherent solid polymeric lubricating film is deposited on a ferrous metal surface to afford such protection are reported in technical publications entitled "In Situ Formation of Solid Lubricating Films from Conventional Mineral, Oil and Ester Solid Lubricants", authored by M. deGouvea Pinto, J. L. Duda, E.E. Graham and E.E. Klaus, ASLE proceedings, 3rd International Conference on Solid Lubrication, ASLESP-14 1984 and "Lubrication from the Vapor Phase at High Temperatures", authored by E.E. Graham and E.E. Klaus, ASLE transactions, volume 29, no. 2 pages 229-234 (1986). As described in said technical publications the metal surfaces are deemed to have a catalytic effect upon the vapor phase reactants whereby surface polymerization of said reactants takes place to produce the protective film. Possibly the absence of comparable metal catalytic agents in ceramic materials has prevented the formation of the protective film in such manner. More particularly, a vapor phase deposition of the same reactants under the same process conditions has thus far only produced non-adherent surface deposits affording no substantial protection to the underlying ceramic substrate.
Improved vapor phase lubrication of ceramic bearing devices with a more adherent organic polymer film is disclosed in a co-pending U.S. patent application Ser. No. 07/488,984 entitled "Ceramic Article Having Wear Resistant Coating", filed Mar. 5, 1990 in the names of E.E. Graham and J.F. Makki. Formation of a tenacious lubricating film is achieved upon treating the uncoated ceramic surface at elevated temperatures with activating metal ions to form a deposit of the activating metal ions on the ceramic surface and thereafter exposing the treated ceramic surface to a vaporized polymer-forming organic reactant at elevated temperatures whereby an adherent solid organic polymer lubricating film is produced on the treated surface. Bearing surfaces formed with crystalline ceramic materials such as silicon nitride and silicon carbide as well as vitreous ceramics such as fused quartz can be provided with a protective coating resistant to dynamic wear conditions up to at least 500.degree. C. and higher in this manner. In one embodiment, activating metal ions comprising a transition metal element selected from the Periodic Table of Elements, to include iron and tin are initially deposited at temperatures of at least 300.degree. C. on the ceramic surface. Formation of the lubricating film on the treated ceramic surface is achieved with vapor deposition again conducted at elevated temperatures of approximately 300.degree. C.-800.degree. C. of various polymer forming organic reactants such as petroleum hydrocarbon compounds, mineral oils, various synthetic lubricants, and to further include tricresyl phosphate (TCP) and triphenyl phosphate.
It remains desirable to provide an effective lubrication of ceramic bearing means when operated at these elevated temperatures under atmospheric conditions by still simpler means. Accordingly, it is one object of the present invention to provide a metal oxide lubrication system for various type mechanical apparatus utilizing ceramic bearing means under such operating conditions, to include gas turbine and aerospace vehicle engines.
It is another object of the present invention to provide means for continuous lubrication of ceramic bearing surfaces with solid metal oxide lubricants formed in situ.
A still further object of the present invention is to provide a novel method for the lubrication of ceramic bearing surfaces with solid metal oxide lubricants.
These and further objects of the present invention will become apparent upon considering the following detailed description of the present invention.